The present invention relates to an information reproducing system for use in an automobile, specifically, an automotive stereo system or an automotive digital audio disk player.
FIG. 1 is a block diagram of a conventional information reproducing system for use in an automobile. In FIG. 1, reference numeral 1 refers to a control unit composed of, for example, a microcomputer which is supplied with a constant voltage from a constant-voltage circuit 2; 3 is a display which indicates the specific state of operations designated by the control unit 1; 4 is an operating unit for driving or otherwise operating a recording medium such as cassette tape in a car stereo; 5 is a detector circuit composed of resistors R.sub.1 and R.sub.2 and a zener diode D for detecting the on or off state of a switch 6 (e.g., an automotive accessory switch) by supplying the control unit 1 with a high- or low-voltage signal in response to the turning on or off of this switch; and 7 is an automotive battery.
The operation of the system shown in FIG. 1 is as follows. The control unit 1 is continuously supplied with a constant voltage from the circuit 2. When the switch) 6 (such as an accessory switch is turned on, a high-voltage signal is applied to the control unit 1 through the detector circuit 5, with the result that the control unit 1 is enabled. If a recording medium such as a cassette (not shown) is loaded, the control unit 1 causes the display 3 to indicate that event and permits the unit 4 to start operating for information reproduction. When the switch 6 is turned off, the control unit 1 is disabled to allow the unit 4 to cease its operation.
As shown in FIG. 2, the voltage of the battery 7 usually drops by a great degree when the engine starter is switched on. Because of this rapid voltage drop, the conventional information reproducing system for use in an automobile is highly likely to cause an error when the engine is started.
FIG. 3 shows a block diagram of another conventional information reproducing system for use in an automobile. In FIG. 3, 1 is a control unit composed of, for example, a microcomputer which is supplied with a constant voltage from a constant-voltage circuit 2; 3 is a display which indicates the specific state of operations designated by control unit 1; 4 is an operating unit for driving or otherwise operating a recording medium such as cassette tape in a car stereo; 5 is a detector circuit composed of resistors R.sub.1 and R.sub.2 and a zener diode D for detecting the on or off state of a switch 6 (e.g., an automotive accessory switch) by supplying the control unit 1 with a high- or low-voltage signal in response to the turning on or off of the switch; 7 is an automotive battery for supplying power; 8 is a voltage detector circuit for detecting the voltage of the battery 7 and supplying the control unit 1 with the detected state, for example, a voltage drop that occurs when the automotive engine starter is switched on; 9 is an operation detector circuit which detects the state of the operation of the unit 4 and supplies this information to the control unit 1; 10 is an equalizer amplifier provided in the path of an information signal reproduced from the recording medium; 11 is a power amplifier; and 12 is a speaker. The amplifiers 10 and 11, as well as the speaker 12, receive power from the battery 7.
The operation of the system shown in FIG. 3 is as follows. If the operating unit 4, receiving an operation command signal from the control unit 1, does not complete a desired operation within a predetermined time, the operation detector circuit 9 senses this failure and sends an error signal to the control unit 1. Then, the control unit 1 inhibits the subsequent operations of the unit 4 on the assumption that trouble has occurred.
As shown in FIG. 2, the voltage of the battery 7 drops so rapidly at the time of engine start that the chance of the occurrence of an error in the operation of the unit 4 is increased. In order to avoid this problem, the system shown in FIG. 3 is so designed that when, at the time of starting the engine, the voltage of the battery 7 drops below a threshold level which could cause erroneous operation of the operating unit 4, the voltage detector circuit 8 detects this drop (FIG. 4, waveforms (a) and (b)), and the control unit 1 mutes the output information signal (FIG. 4, waveform (c)), switches off the display 3 (FIG. 4, waveform (d)), causes the operating unit 4 to stop operating (FIG. 4, waveform (e)), or inhibits the operation detector circuit 9 from performing sensing operation (FIG. 4, waveform (f)).
Because of these design features, even if the operating unit 4 does not complete the intended operation within a predetermined time, the operation detector circuit 9 will not produce an error signal that inhibits operations, pending the restoration of the voltage of the battery, and there will be no problem as the pinch rollers coming to a stop while they are in contact with the capstan.
A delay time t.sub.1 is provided between the occurrence of a signal for the detection of a voltage drop and the production of a signal for muting the output information signal or a signal for switching off the display 3 or operation detector circuit 9, and this delay time prevents erroneous operations that would otherwise occur. The operation of the unit 4 ceases a predetermined time t.sub.2 after the output information signal has been muted. This delay time is provided for the purpose of preventing the reproduction of any abnormal sound that may occur if the operation of the unit 4 is ceased before the muting is effected. When the voltage drop detection signal has disappeared, a delay time t.sub.3 is provided before the display 3 turns on the operating unit 4 or the operation detector circuit 9 is enabled, which delay time is provided for the purpose of preventing an erroneous operation that may otherwise result.
With a view toward enhancing the output power, the recent automotive information reproducing systems use a capacitor of large capacitance in a power source for the power amplifier 11. This, however, causes a drop in the voltage of the battery 7 not only when the engine is started but also when the power amplifier 11 is actuated (see FIG. 7). Therefore, the conventional system shown in FIG. 3 is defective in that the operating unit 4 is also disabled when the power amplifier 11 is turned on.
FIG. 5 is a block diagram of still another conventional information reproducing system for use in an automobile. In FIG. 5, 1 is a control unit composed of, for example, a microcomputer which is supplied with a constant voltage from a constant-voltage circuit 2; 3 is a display which indicates the specific state of operations designated by control unit 1; 4 is an operating unit for driving or otherwise operating a recording medium such as cassette tape in a car stereo; 5 is a detector circuit composed of resistors R.sub.1 and R.sub.2 and a zener diode D for detecting the on or off state of a switch 6 (e.g., an automotive accessory switch) by supplying the control unit 1 with a high- or low-voltage signal in response to the turning on or off of the switch; 7 is an automotive battery; and 9 is an operation detector circuit that supplies the control 1 with the result of detection of the state of operation of the operating unit 4.
The operation of the system shown in FIG. 5 is as follows. The control unit 1 is continuously supplied with a constant voltage from the circuit 2. When the switch 6 is turned on, a high-voltage signal is applied to the control unit 1 through the detector circuit 5, with the result that the control unit 1 is enabled. If a recording medium such as a cassette (not shown) is loaded, the control unit 1 causes the display 3 to indicate that event and permits the unit 4 to start to operate for information reproduction. When the switch 6 is turned off, the control unit 1 is disabled, allowing the unit 4 to stop operating. The system shown above is capable of fairly satisfactory control over the operation and stoppage of the operating unit 4 by turning on or off the switch 6.
If the operating unit 4 does not complete the intended operation within a predetermined time in response to a command from the control unit 1, the operation detector circuit 9 will sense this failure. The control unit 1 then causes the operating unit 4 to stop operating and suspends subsequent operations unless a play button or other operating button is depressed again.
As shown in FIG. 2, the voltage of the battery 7 (FIG. 5) usually drops by a great degree when the engine starter is switched on. Because of this rapid voltage drop, the conventional information reproducing system for use in an automobile is highly likely to cause an error when the engine is started. If this error is detected by the operation detector circuit, the operation of the operating unit is not restored unless it is actuated by manual command. This is inconvenient. Moreover, if the user fails to recognize that the operating unit has stopped in the play mode, the pinch rollers will remain in contact with the capstan and may deform it in an extreme case.